PROJECT ABSTRACT Approximately 4.9 million adults in the US suffer from kidney disease. Current therapies do not provide curative treatments for end state renal disease. Regenerative nephrology holds promise for developing novel therapeutic strategies. The functional unit of the kidney is the nephron, which is derived from a distinct progenitor cell population during embryonic development. A delicate balance of nephron progenitor cell (NPC) self-renewal and differentiation is required to generate a species-appropriate number of nephrons during the course of kidney development. The transcriptional regulator Six2, and transcriptional mediators of the Wnt/?-catenin signaling pathway, Lef/Tcf factors, play critical roles balancing the maintenance and commitment of NPCs. In this, Six2 is essential for NPC self-renewal and interacts with Lef/Tcf factors. ?-catenin accumulation acts to switch the code of Lef/Tcf factor engagement at differentiation targets from a repressor to activator transcriptional signature. The overarching hypothesis tested in this proposal is that ?-catenin accumulation switches the Lef/Tcf regulatory signature from an OFF to ON state. In AIM 1, I will perform loss of function experiments to unravel the mechanism of action of ?-catenin concentration dependent Tcf/Lef factor engagement resulting in transcriptional changes. In AIM 2, I will perform multi-protein proteomic analysis to define multiprotein complexes surrounding ?-catenin with immunoprecipitation and mass spectrometry-based affinity proteomics Mechanistic understanding of Wnt/?-catenin signaling in concert with identified binding partners will facilitate the derivation of nephron-like cell types in vitro and ultimately regenerative therapies for renal diseases.